Thermally actuated switch



Sept. 27, 1955 J. A. WOLFF THERMALLY ACTUATED SWITCH Filed Jan. 16, 1952 INVENTOR.

rfog n 0?. M0 if] flour. JALZZZlu [alum Wig/5 United States Patent THERMALLY ACTUAT ED SWITCH John A. Wolff, Milwaukee, Wis, assignor to Milwaukee Gas Specialty Company, Milwaukee, Win, a corp-aration of Wisconsin Application January 16, 1952, Serial No. 266,626

23 Claims. (Cl. 208-140) This invention relates, in general, to electric switches, and has particular relation to thermally actuated switches of the type comprising an expansible and contractible container containing a volatile fluid and contacts arranged to be separated and brought into contact by change in volume of the fluid.

While the particular device which I shall describe hereinafter in connection with the drawings is adapted for use for regulating automatically the temperature produced by heating apparatus, especially heating apparatus under thermoelectric control, and more particularly, for maintaining the temperature of a room or other space at a definite temperature, it is to be understood that the device may be used as a limit switch for terminating the operation of heating apparatus at a high temperature limit or for starting the operation of heating apparatus at a low temperature limit. Within the broader aspects of the invention, the device may also be used for controlling other apparatus, or for making, breaking, or changing the connections in one or more electric circuits for heaters or other devices as suitable or desired.

One of the main objects of the present invention is to provide a thermally actuated switch of the class described which will fail-safe (i. e., open the circuit by separating the contacts) if a leak occurs in the expansible and contractible container.

Another and more specific object is to provide for accomplishing this fail-safe feature by employing within the expansible and contractible container a sub-atmospheric fill to provide within the container, for example, at normal room temperature, a pressure somewhat below atmospheric pressure so that if a leak occurs, the atmospheric pressure which enters the container will cause separation of the contacts therein.

Another more specific object is to accomplish the failsafe feature by providing contacts which are arranged not only to be separated by expansion of the container in the normal operation of the device but which contacts will also be separated to open the circuit and thereby fail-safe if a leak occurs and a fill is employed having, at normal room temperatures, a pressure somewhat above atmospheric pressure so that the pressure within the container is reduced by such leak with accompanying contraction of the container.

Another object is to provide the fail-safe feature in conjunction with a device that may be tilted or jarred without affecting the electrical connection.

Another object is to provide the fail-safe feature in conjunction with a device in which a solid contact-tosolid contact make and break arrangement is provided within the expansible and contractible container and in which the volatile or other expansible and contractible fluid acts not only to produce expansion and contraction of the container, but, by disposition of the contacts therein to keep the contacts clean.

Further objects and advantages, and numerous adaptations of the invention will appear from the following ice detailed description, taken in connection with the accompanyingdrawings.

In the drawings:

Figure 1 is a side elevational view of a thermostat embodying the present invention;

Figure 2 is a longitudinal axial section taken on the line 22 of Figure l and showing fragmentarily adjustment means for the thermostat;

Figure 3 is a more or less diagrammatic axial sectional view showing another embodiment of the invention with the contacts in contact;

Figure 4 is a view similar to Figure 3 showing the contacts separated by expansion of the bellows; and

Figure 5 is another view similar to Figure 3 showing the contacts separated by contraction of the bellows.

Referring first to Figures l2, in the embodiment of the invention therein illustrated the expansible and contractible container is in the form of a flexible metallic bellows or Sylphon 1 having a flexible corrugated side wall 2 provided at one end with an integral cup-shaped part 3. The cup-shaped part 3 has an integral end wall 4 provided with an axial opening 6. At its opposite end the bellows 1 has an end wall 7 provided with an axial opening 8.

A stamped metallic bracket 9 has a base 10 and integral outstanding legs 11 and 12 which embrace or straddle the bellows l endwise. The end wall 4 is fixedly secured to the leg 12 and in good contact therewith, for example, by a flanged sleeve 13 within which is secured a glass or other suitable seal 14 which seals the adjacent end of the bellows. A conductor 15 extends into the interior of the bellows 1 through the seal 14 and carries within the bellows a contact 16 which may be soldered or otherwise secured to the inner end of the conductor 15 and constitutes the fixed contact of the thermostat.

A contact stem 17 has integral therewith and disposed within the bellows 1 in axial alignment with the contact 16 a contact 18 which constitutes the movable contact of the device. The stem 17 extends out through the opening 8 and through an opening in a metallic leaf spring 19 adjacent which the stem 17 is attached to the spring 19. The stem 17 also extends through an enlarged opening in the leg 11 with ample clearance therebetween to receive, for example, a bellows-adjusting member as will hereinafter appear. An insulating sleeve 26 closely surrounds the stem 17 and is interposed endwise between the spring 19 and the end wall 7 of the bellows. The sleeve 20 constitutes a spacer between the spring 17 and the end wall 7 of the bellows 1.

The spring 19 is attached, for example, by rivets or the like 21 to the leg 11 of the bracket 9. The bracket 9 has strengthening ribs 22 stamped inwardly therefrom. These ribs 22 give rigidity to the bracket 2 and the spring 19 is flexible and, by attachment to the stem 17, guides the movable end of the bellows for substantially linear movement. The leg 12 is wider than the leg 11 and has in its extending portions apertures 23 which may receive, for example, tie rods (not shown) where the thermostat is combined with an adjustment mechanism of the type to be hereinafter described.

The base of the bracket 9 has apertures 24 for receiving, for example, one or more screws (not shown) for mounting the bracket and connecting a terminal bracket (not shown) in circuit with the bracket 9. For purposes of illustration, a lead conductor 26 of an electric circuit 27 which the thermostat is adapted to open and close is connected to the bracket 9. The conductor 23 forming the other side of the electric circuit is connected to the conductor 15. Thus when the movable contact 18 is in contact with the fixed contact 16, the electric circuit is completed, for example, from the conductor 26 through the bracket 9 and wall of the bellows 1 to the contact 3 18 and thence through the engaging contact 16 and conductor to the conductor 28.

The interior of the bellows 1 is filled with a volatile fluid which is adapted to expand and contract with accompanying expansion and contraction of the bellows 1 upon changes in ambient temperature at the position at which the bellows 1 is disposed. In accordance with this embodiment of the present invention, the fluid employed within the container, at normal room temperatures, has or provides within the container a pressure somewhat below atmospheric pressure. Thus if a leak occurs in the wall of the container, the entry of the greater atmospheric pressure through the leak will expand the container with accompanying separation of the contact 13 from the contact 16. In case of a leak, the device therefore will always fail safe by opening the circuit controlled by the contacts 16 and 18.

Ether, methylene chloride, trichloro trifiuoro ethane and isopentane are illustrative examples of suitable subatmospheric fills that may be employed according to this embodiment of the invention. The expansible and contractible container may also be filled with isopropyl alcohol, for example, for 180 F. maximum setting, N-propyl alcohol for a 200 F. maximum setting, isobutyl alcohol for a 220 F. maximum setting, N-butyl alcohol for a 240 F. maximum setting, isoamyl alcohol for a 260 F. maximum setting, M-xylene for a 280 F. maximum setting, or with P-cymene for a 340 F. maximum setting. Other sub-atmospheric fills may, of course, be employed within the scope of the broader aspects of this form of the invention.

It will be noted from the foregoing that some of the fills mentioned for illustration have higher boiling points than other fills. This makes it possible by selection of a subatmospheric fill with the desired boiling point to provide by the boiling point of the fill for separation of the contacts at the desired upper temperature limit. Of course, variations in the temperature at which the contacts separate may be accomplished by adjustment mechanism, for example, of the type to be hereinafter described.

In the use of the thermally actuated switch shown in Figures 1-2, it is positioned in the room or other space or where it will be otherwise subjected to the temperature which it is desired to maintain or to the temperature at which the switch is intended to open and close.

Where, for example, the device is used as a thermostat for regulating automatically the temperature produced by heating apparatus to maintain the temperature of a room or space at a definite temperature, it is positioned in such room or space where it will be subject to the ambient temperature therein. When the ambient temperature rises above the temperature for which the device is set, the volatile fluid within the bellows 1 expands with the result that the bellows expands endwise causing the contact 18 to move out of contact with the contact 16. This opens the circuit shown diagrammatically at 26, 28 which results in shutting off the heating action of a heater (not shown), for example, by shutting off the flow of fuel to the burner of the heater.

When the ambient temperature drops below the temperature for which the thermostat is set, the volatile fluid within the bellows 1 contracts with accompanying endwise contraction of the bellows, for example, under the action of a spring 30 which is shown confined endwise between a cup 32 and a plate 33.

If, as already pointed out, a leak occurs in the wall of the container, the entry of the greater atmospheric pressure through the leak will expand the container endwise with accompanying separation of the contact 18 from the contact 16 to open the circuit and make the device fail safe.

Temperature adjusting means of the type disclosed or of any other suitable or preferred type may be provided for adjusting the temperature for which the thermostat is set. Suffice it for purposes of the present application to state that a cam shown fragmentarily at 35 may, when turned, push a stem 36 downwardly (Figure l) to compress the spring 30 which, by its bearing against the plate 33, forces an adjustment screw 37 downwardly to put pressure on the end Wall 7 of the bellows. The adjustment screw 37 has screwed engagement with a second threaded part 38 and the parts 37 and 38 can be turned relative to each other to effect a factory adjustment of the device.

The bellows 1 may be provided with a piece of copper tubing 40 having an angular end opening through the end wall 7 through which the desired fill may be introduced into the bellows. After the fill is introduced the outer end of the tube 40 may be pressed together or deformed to close the same at 42.

In the embodiment of the invention shown in Figures 3-5, the expansible and contractible container is in the form of a metallic flexible bellows or Sylphon having a flexible corrugated side wall 51.

The conductor 52 enters the container through the end wall 53 and carries within the container 50 a solid contact 54 which constitutes, for example, the fixed contact. The conductor 52 may be secured to the end wall 53 of the container at 55 and may, if desired, be insulated therefrom. A conductor 56 enters the container through the opposite end wall 57 and carries within the container 50 a solid contact 58. The conductor 56 may be secured at 59 to the end Wall 57 which constitutes the movable end of the container and may, if desired, be insulated therefrom. One lead conductor 60 of the electric circuit which the thermally actuated switch is adapted to open and close may be connected to the conductor 52. The other lead conductor 61 of the electric circuit may be connected as shown more or less diagrammatically to the other conductor 56. The bellows 5t contracts under the influence of a loading spring 62 interposed between the movable end of the bellows and an abutment plate 63. The abutment plate 63 may be adjustable or other adjustment means may be provided for adjusting the action of the spring 62 and thereby the temperature for which the device is set.

The interior of the bellows 50 is filled with a volatile fluid which is adapted to expand and contract with accompanying expansion and contraction of the bellows upon changes in ambient temperature at the position at which the bellows is disposed. Thus the volatile fluid should be so selected that for any given temperature range, the vapor pressure change per degree Fahrenheit of the particular fill should be high enough so atmospheric pressure changes do not seriously shift the control point of the thermostat. However, the upper limit of pressure developed in the bellows should not exceed its mechanical limitations. Illustrative of such fluid fills are butane (which is a colorless gaseous c0mpoundB4H1oof the aliphatic hydrocarbon or marsh-gas series) which at F. will exert a pressure of approximately 31 pounds; isobutane which at 70 F. will exert a pressure of approximately 45 pounds; sulphur dioxide (S02), which at 70 F. will exert a pressure of approximately 50 pounds; methyl chloride (CHsCl), which at 70 F. will exert a pressure of approximately 72 pounds; 8-12 or Freon (CClzFz), which at 70 P. will exert a pressure of approximately pounds; and propane (CzHs), which at 70 F. will exert a pressure of approximately pounds.

The foregoing fills, at normal room temperatures, have an internal pressure somewhat above atmospheric pressure and hence if a leak occurs it will bring the pressure down within the bellows. Other fills are, of course, contemplated within the scope of this embodiment of the invention.

When the ambient temperature drops below the temperature for which the thermostat is set, the volatile fluid within the belows S0 contracts with accompanying endwise contraction of the bellows, for example, under the action. of the spring 62. This brings the contact 58 into contact with the contact 54 which closes the electric circuit and starts the heating apparatus.

When the ambient temperature rises above the temperature for which the device is set, the volatile fluid within the bellows 50 expands with the result that the bellows expands endwise causing the contact 58 to move out of contact with the contact 54, for example, to the position shown more or less diagrammatically in Figure 4. This opens the circuit which includes the lead conductors 6th and 61 which results in shutting off the heating action of the heater (not shown), for example, by shutting oif the flow of fuel to the burner.

If with the contacts 54 and 58 in contact as shown in Figure 3, a leak occurs in the bellows 50, the greater pressure within the bellows will leak out reducing the pressure within the bellows which will contract moving the contact 58, for example, from the position shown in Figure 3 to open circuit position shown in Figure 5. If the leak occurs with the contact 58 out of contact with the contact 54 as shown in Figure 4, the contact 58 will slide past the contact 54 to open circuit position as shown in Figure 5. Thus this device will always fail safe notwithstanding the presence of a fluid within the bellows which at normal room temperatures has a pressure somewhat higher than atmospheric pressure.

It will be noted that in the form of the invention shown in Figures 3-5, separation of the contacts 54 and 58 by expansion of the fluid within the bellows is accomplished by expansion of the bellows whereas separation of the contacts 54 and 5% in the event a leak occurs is accomplished by contraction of the bellows.

if desired, the bellows 50 may be responsive to changes in temperature at a location remote from the bellows, for example, by providing a bulb 65 for positioning in such remote location. The interior of the bulb 65 is connected with the interior of the bellows 50 by a tube 66 the interior of the bulb 6S and the tube 66 being filled with the volatile fluid which fills the interior of the bellows 50. This enables positioning the bellows remote from the location to the temperature of which the device is responsive.

The embodiments of the invention shown in the draw ings are for illustrative purposes only and it is to be expressly understood that said drawings and the accompanying specification are not to be construed as a definition of the limits or the scope of the invention, reference being had to the appended claims for that purpose.

I claim: I

1. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in ambient temperature with accompanying expansion and contraction of said enclosure and movement of the movable end thereof, and a pair of cooperating contacts within said enclosure electrically engageable with each other, one of said contacts being movable with said movable end away from electrical engagement with the other contact upon expansion of said enclosure, said movable contact being movable toward electrical engagement with the other contact upon contraction of said enclosure, and said movable contact also being movable with said movable end away from electrical engagement with the other contact in the event of leakage of said enclosure to provide safe failure.

2. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of the movable end of said enclosure, a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction away from its cooperating contact upon expansion of said enclosure and tending to move with said movable end toward its cooperating contact upon contraction of said enclosure, said contact which is movable with said movable end tending to move with said movable end in a direction away from its cooperating contact in the event of leakage of said enclosure, and means normally biasing said contact movable with the movable end of the enclosure into engagement with its cooperating contact.

3. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of the movable end of said enclosure, a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction away from its cooperating contact upon expansion of said enclosure and tending to move with said movable end toward its cooperating contact upon contraction of said enclosure, said contact which is movable with said movable end tending to move with said movable end in a direction away from its cooperating contact in the event of leakage of said enclosure, means normally biasing said contact movable with the movable end of the enclosure into engagement with its cooperating contact, and temperature adjusting means comprising means for adjusting the bias of said biasing means.

4. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in ambient temperature with accompanying expansion and contraction of said enclosure and movement of the movable end thereof, and a pair of cooperating contacts within said enclosure electrically engageable with each other and at all times immersed and bathed in said volatile fill, one of said contacts being movable with said movable end away from electrical engagement with the other contact upon expansion of said enclosure, said movable contact being movable toward electrical engagement with the other contact upon contraction of said enclosure, and said movable contact also being movable with said movable end away from electrical engagement with the other contact in the event of leakage of said enclosure to provide safe failure.

5. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in ambient temperature with accompanying expansion and contraction of said enclosure and movement of the movable end thereof, and a pair of cooperating contacts within said enclosure electrically engageable with each other, and each being of substantially rigid construction, one of said contacts being movable with said movable end away from electrical engagement with the other contact upon expansion of said enclosure, said movable contact being movable toward electrical engagement with the other contact upon contraction of said enclosure, and said movable contact also being movable with said movable end away from electrical engagement with the other contact in the event of leakage of said enclosure to provide safe failure.

6. A temperature responsive device comprising a hermetically sealed enclosure having a movable end and expansible and contractible in response to changes in ambient temperature, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in said ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of said movable end of said enclosure, and a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction way from electrical engagement with its cooperating contact upon expansion of said enclosure and tending to move with said movable end and in a direction toward electrical engagement with its cooperating contact upon contraction of said enclosure, said volatile fill, at normal room temperatures, having a pressure below atmospheric pressure, whereby in the event of leakage of said enclosure entry of greater atmospheric pressure through the leak will cause said contact which is movable with said movable end to tend to move with said movable end in a direction away from electrical engagement with its cooperating contact with accompanying safe-failure of said device.

7. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in the ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of said movable end of said enclosure, a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction away from its cooperating contact upon expansion of said enclosure and tending to move with said movable end and in a direction toward its cooperating contact upon contraction of said enclosure, said volatile fill, at normal room temperatures, having a pressure below atmospheric pressure, whereby in the event of leakage of said enclosure entry of greater atmospheric pressure through the leak causes said contact which is movable with said movable end to tend to move with said movable end in a direction away from its cooperating contact with accompanying safe-failure of said device, and means normally biasing said contact movable with the movable end of the enclosure into engagement with its co-operating contact.

8. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure Whose vapor pressure increases and decreases upon rise and drop in the ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of said movable end of said enclosure, a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction away from its cooperating contact upon expansion of said enclosure and tending to move with said movable end and in a direction toward its cooperating contact upon contraction of said enclosure, said volatile fill, at normal room temperatures, having a pressure below atmospheric pressure, whereby in the event of leakage of said enclosure entry of greater atmospheric pressure through the leak causes said contact which is movable with said movable end to tend to move with said movable end in a direction away from its cooperating contact with accompanying safe-failure of said device, means normally biasing said contact movable with the movable end of the enclosure into engagement with its cooperating contact, and temperature adjusting means comprising means for adjusting the bias of said biasing means.

9. A temperature responsive device according to claim 6 wherein the cooperating contacts are at all times immersed and bathed in the volatile fill within said enclosure.

lO. A temperature responsive device according to claim 6 wherein each of the cooperating contacts within said enclosure is of substantially rigid construction.

11. A temperature responsive device comprising a hermetically sealed enclosure having a movable end and expansible and contractible in response to changes in ambient temperature, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in said ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of said movable end of said enclosure, and a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction toward electrical contact with its cooperating contact upon contraction of said enclosure due to a drop in ambient temperature and tending to move in one direction out of electrical contact with its cooperating contact upon expansion of said enclosure due to a rise in ambient temperature, said contact which is movable with said movable end tending to move with said movable end and in another direction out of electrical contact with its cooperating contact in the event of leakage of said enclosure to provide safe failure of the device.

12. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in the ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of said movable end of said enclosure, a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction toward engagement with its cooperating contact upon contraction of said enclosure due to a drop in ambient temperature and tending to move in one direction away from its cooperating contact upon expansion of said enclosure due to a rise in ambient temperature, said contact which is movable with said movable end tending to move with said movable end and in another direction away from its cooperating contact in the event of leakage of said enclosure, and means normally biasing said contact movable with the movable end of the enclosure into engagement with its cooperating contact.

13. A temperature responsive device comprising an expansible and contractible hermetically sealed enclosure having a movable end, a volatile fill sealed within said enclosure whose vapor pressure increases and decreases upon rise and drop in the ambient temperature with accompanying expansion and contraction of said enclosure and accompanying movement of said movable end of said enclosure, a pair of cooperating contacts within said enclosure one tending to move with said movable end and in a direction toward engagement with its cooperating contact upon contraction of said enclosure due to a drop in ambient temperature and tending to move in one direction away from its cooperating contact upon expansion of said enclosure due to a rise in ambient temperature, said contact which is movable with said movable end tending to move with said movable end and in another direction away from its cooperating contact in the event of leakage of said enclosure, means normally biasing said contact movable with the movable end of the enclosure into engagement with its cooperating contact, and temperature adjusting means comprising means for adjusting the bias of said biasing means.

14. A temperature responsive device according to claim 11 wherein the cooperating contacts are at all times immersed and bathed in the volatile fill within said enclosure.

15. A temperature responsive device according to claim 11 wherein each of the cooperating contacts within said enclosure is of substantially rigid construction.

16. A condition responsive device comprising a hermetically sealed enclosure expansible and contractible in response to changes in a condition, a pair of cooperating contacts within said enclosure, at least one of said contacts tending to move relative to the cooperating contact directly and continuously with changes in said condition, and a volatile fill sealed within said enclosure and having, at normal room temperatures, a pressure below atmospheric pressure.

17. A condition responsive device comprising a her metically sealed enclosure expansible and contractible in response to changes in a condition, a volatile fill within said enclosure, and a pair of cooperating contacts within said enclosure, at least one of said contacts being movable and having electrical engagement with its cooperating contact in an intermediate position said movable contact tending to move in one direction away from electrical engagement with its cooperating contact upon expansion of said enclosure due to one change in condition and tending to move in the opposite direction away from electrical engagement with its cooperating contact upon contraction of said enclosure due to leakage of said volatile fill from said enclosure.

18. A condition responsive control device comprising an hermetically sealed expansible and contractible enclosure, a movable control member having an operating position and connected to said enclosure for movement away from said operating position to a safety position on expansion of said enclosure, a condition responsive expansible and contractible volatile fluid fill sealed within said enclosure, the connection of said control member to said enclosure also efiecting movement of said control member away from said operating position in the event of leakage of said enclosure, and biasing means normally exerting a contractile force on said enclosure to thereby bias said control member toward said operating position.

19. A condition responsive control device comprising an hermetically sealed expansible and contractible enclosure having a movable wall, a movable control member having an operating position and connected to said rnovable wall for movement therewith away from said operating position to a safety position on expansion of said enclosure, a condition responsive expansible and contractible volatile fluid fill sealed within said enclosure, said control member also being movable with said movable wall away from said operating position in the event of leakage of said enclosure, and means normally biasing said control member toward said operating position.

20. A condition responsive control device comprising an hermetically sealed expansible and contractible enclosure, a condition responsive expansible and contractible volatile fluid fill sealed within said enclosure, said fill normally having a vapor pressure below atmospheric pressure, at least one control member connected to said enclosure for movement with expansion and contraction thereof in response to changes in the condition, and external biasing means exerting a contractile force on said enclosure.

21. A condition responsive control device comprising an hermetically sealed expansible and contractible enclosure, a movable control member having an operating position and connected to said enclosure for movement to a safety position on expansion of said enclosure, biasing means exerting a contractile force on said enclosure to thereby bias said control member toward said operating position, and a condition responsive expansible and contractible volatile fluid fill sealed wthin said enclosure, said fill normally having a vapor pressure below atmospheric pressure, wherefore in the event of a leak in said enclosure, the entry of greater atmospheric pressure into the enclosure effects expansion thereof against said bias and movement of the control member to said safety position.

22. A condition responsive control device comprising an hermetically sealed expansible and contractible enclosure, a movable control member having an operating position and connected to said enclosure for movement to a safety position on expansion of said enclosure, a condition responsive expansible and contractible volatile fluid fill sealed within said enclosure, said fill normally having a vapor pressure below atmospheric pressure, wherefore in the event of a leak in said enclosure, the entry of greater atmospheric pressure into the enclosure effects expansion thereof and movement of the control member to said safety position, and means biasing said control member toward said operating position.

23. A condition responsive control device comprising an hermetically sealed expansible and contractible enclosure, a condition responsive expansible and contractible volatile fluid fill for said enclosure, and a movable control member having an intermediate operating position, said control member being connected to said enclosure for movement in one direction away from said intermediate position to a first safety position on expansion of said enclosure, said control member also being movable in another direction away from said intermediate position to a second safety position on contraction of said enclosure, wherefore in the event of a leak in said enclosure said control member is moved to one of said safety positions.

References Cited in the file of this patent UNIT ED STATES PATENTS 243,345 Lungen June 21, 1881 308,293 Tubbs Nov. 18, 1884 360,823 Singer Apr. 5, 1887 1,109,996 Kuhlman Sept. 8, 1914 

